Editorial. Special Issue: “6th International Conference on Tunable Diode Laser Spectroscopy”

ISSN:0946-2171ISSN:1432-0649ISSN:0721-7269ISSN:0340-379

Nitrogen-Pressure Shifts in the v3 Band of Methane Measured at Several Temperatures between 300 and 90 K

Remote sensing of the Earth's atmosphere requires accurate knowledge of spectroscopic line parameters for the molecules investigated. Knowledge of the temperature dependence of these parameters is also essential if agreement, at the noise level, between calculated and experimental data is to be achieved. The authors recently published results of nitrogen broadening measurements in the v3 band of 12CH4 using the 5.37 m long absorption path length all-copper Herriott cell. The temperature dependent line parameters determined in the laboratory were applied to fit a portion of the atmospheric spectrum recorded with a balloon-borne remote sensing FTIR instrument, called the Limb Profile Monitor of the Atmosphere, and operating in absorption against the sun. Since the authors had a relatively complete series of data for the P(9) transition in the v3 band of 12CH4, the A2 1 as well as the F2 1, F1 1 and A1 1 lines recorded at different pressures and at four temperatures between 300 and 90 K, we reanalyzed the data to derive pressure shift information at different temperatures. The temperatures for which data were collected and analyzed are 298, 140 and 90K. The high precision pressure shift data obtained here over a large range of temperature demonstrate the ability of our experimental arrangement to address specific questions on a given spectral window like in the balloon experiment or in a satellite project, for example

Experimental He-pressure broadening for the R(10) and P(2) lines in the ν 3 band of 13CO 2, and experimental pressure shifts for R(10) measured at several temperatures between 300 K and 100 K

International audienceHelium broadening coefficients for the R(10) and the P(2) lines in the ν 3 band of 13CO 2 have been measured over a large range of temperature (70 K-300 K). Helium pressure shifts for the R(10) line at several temperatures between 100 K and 300 K have also been determined. These measurements were obtained with a cold Herriott cell, using the collisional cooling technique to reach the lowest temperatures. They provide an extended dataset for the temperature dependence of widths and shifts. This dataset was compared to theoretical He-broadening coefficients combining quantum scattering calculations and the latest potential energy surface for the system He-CO 2 from Korona et al. [T. Korona, R. Moszynski, F. Thibault, J.-M. Maunay, B. Bussery-Honvault, J. Boissoles, P.E.S. Wormer, J. Chem. Phys. 115 (2001) 3074-3084]

Performance of a Herriott Cell, Designed for Variable Temperatures between 296 and 20 K

We designed, fabricated and tested a multipath Herriott cell (or off-axis spherical mirror interferometer) to achieve low temperature absorption measurements. The cell is fabricated entirely from copper and the 15 cm radius of curvature copper mirrors have gold coated reflective surfaces. The cell was tested at temperatures between 296 and 30 K with a folded absorption path length of 5.37 m utilizing a lead salt tunable diode laser. Short term temperature stability (1 h) of the Herriott cell is better than 0.005 K under normal operating conditions with a temperature uniformity better than 0.01 K (not measurable). The cell was tested by performing collisional cooling experiments on 13C16O2 in helium at temperatures between 70 and 20 K and by performing more traditional pressure broadening and shift measurements on molecular infrared absorption lines at temperatures between 300 and about 80 K on 13C16O2 methane

Measurement of the Temperature Dependence of Line Mixing and Pressure Broadening Parameters between 296 and 90 K in the v3 band of 12CH4 and their Influence on Atmospheric Methane Retrievals

We measured the temperature dependence of the nitrogen broadening, narrowing and line-mixing coefficients of four lines of the P9 manifold in the v3 band of 12CH4 for atmospheric purposes. The data were collected using our tunable diode laser (TDL) spectrometer with active wavenumber control coupled to a newly developed cold Herriott cell with a path length of 5.37 m and a temperature uniformity of better than 0.01 K along the cell. We recorded and analyzed spectra recorded at sample temperature between 90 K and room temperature. We have investigate the influence of our new results in the inversion model used to retrieve methane profiles from atmospheric spectra; our new results make it possible to retrieve significantly more precise methane profiles. The atmospheric spectra we utilized were obtained by several of us with a balloon-born Fourier Transform infrared experiment in a limb configuration. Differences up to 7% on the retrieved volume mixing ratio were found compared to an inversion model using only HITRAN04 spectroscopic parameters

SELF- AND AIR-BROADENING OF 12^{12}C16^{16}O, 13^{13}C16^{16}O AND 12^{12}C18^{18}O AT 2.3 μ\mum

Author Institution: The College of William and Mary, Williamsburg, VA 23187; Science Directorate, NASA Langley Research Center, Hampton, VA 23681; Dept. of Physics, Astronomy and Geophysics, Connecticut College, New London, CT 06320; Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Dr.,Pasadena, CA 91109High resolution (0.005 cm$^{-1}$) absorption spectra of CO and two of its isotopologues ($^{13}$CO and C$^{18}$O) were recorded between 3550 and 5250 cm$^{-1}$ using the Bruker IFS-125HR Fourier transform spectrometer (FTS) located at the Jet Propulsion Laboratory (JPL) and a specially designed and built coolable 20.38 cm long absorption cell nderline{\textbf{262}} (2010) 122-134.} placed within the sample compartment of the FTS. More than 50 spectra of both pure and air-broadened samples of CO, $^{13}$CO and C$^{18}$O were recorded at various temperatures from 150 K to 298 K, with maximum total pressures up to $\sim$700 Torr. A multispectrum nonlinear least squares spectrum fitting technique nderline{\textbf{53}} (1995) 705-721.} was used to determine the spectral line shape parameters including speed dependence, Lorentz halfwidth coefficients, pressure-induced shift coefficients, and off-diagonal relaxation matrix element coefficients for line mixing. These line shape parameters were obtained for both self- and air-broadening, and temperature dependences of these parameters were determined where possible. As previously done in studies of CO$_2$, nderline{\textbf{242}} (2007) 90-117.} rather than retrieving individual line positions and intensities, we constrained them to their theoretical relationships, including Herman-Wallis terms, determining only the band intensities and rovibrational constants. The results are discussed and compared with values reported in the literature

CLOSED-CYCLE HE-COOLED ABSORPTION CELLS DESIGNED FOR A BRUKER IFS-125HR: FIRST RESULTS BETWEEN 79 K AND 297K

Author Institution: Dept. of Physics, Astronomy and Geophysics, Connecticut College, New London, CT 06320, U.S.A.; Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Dr.,Pasadena, CA 91109, U.S.A.; Science Directorate, NASA Langley Research Center, Hampton, VA 23681, U.S.A.; The College of William and Mary, Williamsburg, VA 23187, U.S.A.Gas absorption cells specifically designed to achieve stable temperatures down to $\sim$70 K to fit inside the sample compartment of an evacuated Bruker (IFS-125HR) Fourier Transform spectrometer (FTS) have been developed at Connecticut College, and tested at the Jet Propulsion Laboratory (JPL). In operation, the temperature-controlled cooling by a closed-cycle helium refrigerator achieved a temperature stability of $\pm$0.01 K. The unwanted absorption features initially observed from cryo-deposits formed on the outside cell windows were eliminated by adding an internal vacuum shroud box around the coolable cell to isolate it from residual gases in the evacuated FTS chambers. The effects of vibrations arising from the closed-cycle helium refrigerator upon the FTS spectra were characterized. Using this set up, high resolution spectra of several methane isotopologues (such as $^{12}$CH$_4$, $^{13}$CH$_4$ and $^{12}$CH$_3$D) broadened by N$_2$, were recorded in the 1230 to 1850 cm$^{-1}$ spectral region. Such data are needed to characterize the temperature dependence of line shapes at very low temperatures for remote sensing of outer planets and their moons. Results from the initial analysis of the R(2) manifold of the $\nu_4$ fundamental band of $^{13}$CH$_4$ are discussed to examine whether the N$_2$-broadened half width coefficients follow a simple exponential temperature-dependence over the entire 80 - 296 K temperature range. This initial test was very successful, proving that a high precision Fourier transform spectrometer can be easily configured for spectroscopic studies at very low temperatures relevant to planetary atmospheres

PERFORMANCE OF A CRYOGENIC 21 METER-PATH COPPER HERRIOTT CELL VACUUM COUPLED TO A BRUKER 125HR SYSTEM

Author Institution: Dept. of Physics, Connecticut College, New London, CT 06320; Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Dr.,Pasadena, CA 91109; Science Directorate, NASA Langley Research Center, Hampton, VA 23681; Dept. of Physics, The College of William and Mary, Williamsburg, VA 23187Accurate modeling of planetary atmospheres requires a detailed knowledge of the temperature and pressure dependence of spectroscopic line parameters of atmospheric molecules. With this requirement in mind, a new Herriott cell having a 21 meter folded absorption path was designed and fabricated with Oxygen-Free High Conductivity (OFHC) copper body and gold coated OFHC copper mirrors to operate for the first time with a broad-band Fourier transform spectrometer. The cell, enclosed in an isolated vacuum box, is cooled by a CTI Cryogenics, Inc. model 1050 closed-cycle helium refrigerator which also cryopumps the vacuum box. The temperature of the cell is monitored by a silicon temperature sensor and regulated by a Lakeshore model 331 temperature controller. The new cell system was integrated to the JPL Bruker model 125HR interferometer with transfer optics which are fully evacuated to 12 mTorr (the pressure inside the interferometer). The optics were through-put matched for entrance apertures smaller than 2 mm. The system has successfully operated for several months at gas sample temperatures between 75 and 250 K with extremely good stability to obtain spectra of methane, carbon dioxide, and oxygen bands between 0.76 and 3 $\mu$m. We present the characterization and performance of the Herriott cell system and preliminary analyses of newly recorded spectra